As the haze pollution issue is getting more and more severe at present, vehicle exhaust is gaining more and more attention. It is reported that the diesel vehicle may be responsible for this issue to the most extent. Then, to reduce the haze pollution, one out of the key factors is to improve the product standard of diesel oil, whereby rendering the diesel oil deep hydrodesulfurization technology more and more important under the current situation.
Sulfur-containing compounds in diesel oil mainly include fatty sulfides, thioethers, dibenzothiophenes, alkyl benzothiophenes and alkyl dibenzothiophenes, wherein thiophenes like dibenzothiophenes, alkyl benzothiophenes and alkyl dibenzothiophenes (hereinafter collectively referred to as hardly desulfurizating compound) are relatively difficult to be removed, and among them, thiophenes characterized by a complicate chemical structure and significant steric hindrance like 4,6-dimethyl dibenzothiophene and 2,4,6-trimethyl dibenzothiophene, are most difficult to be removed. Diesel oil deep hydrodesulfurization mainly intends to remove these hardly desulfurizating compounds, however, these hardly desulfurizating compounds, if with a conventional hydrodesulfurization technology, are hardly to be removed even at elevated temperatures and pressures. For this reason, a diesel oil hydrodesulfurization (especially deep hydrodesulfurization) technology may have to be based on a reaction mechanism significantly different from the conventional hydrodesulfurization, which necessitates specially designing a diesel oil hydrodesulfurization catalyst.
In addition to diesel oil, other heavy distillate oils need a similar deep hydrodesulfurization as well.
Chinese patent CN99103007.9 discloses a hydrotreating catalyst, comprising WO3 and/or MoO3, NiO and CoO supported onto an alumina carrier. The catalyst contains a relatively lower amount of metal but exhibits a relatively high activity at lowered temperatures, especially suitable for hydrodesulfurization of light-end products.
Chinese patent CN99113281.5 discloses a hydrotreating catalyst, which comprises alumina or silica-containing alumina as the carrier, and W, Mo, Ni as the active components, and further phosphorus as an auxiliary component. The catalyst exhibits a significantly high hydrodenitrification activity.
The prior art hydrotreating catalysts have been identified as conventional hydrodesulfurization catalyst, and therefore can not be effectively used for the hydrodesulfurization of heavy distillate oils (especially diesel oil). Therefore, there remains a need in the prior art for a hydrotreating catalyst, which is especially suitable for the hydrodesulfurization (especially deep hydrodesulfurization) of heavy distillate oils (especially diesel oil).